The disclosure of Japanese Patent Application No. HEI 11-230781 filed on Aug. 17, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a vehicle deceleration unit performing deceleration control of a vehicle and, more particularly, to a vehicle deceleration unit and a vehicle deceleration method wherein a control amount relating to deceleration of the vehicle is determined based on the turning state of the vehicle.
2. Description of the Related Art
When decelerating a vehicle, hydraulic pressure is generated through depression of a brake pedal by a driver. This hydraulic pressure is directly transmitted to wheels and inhibits the wheels from rotating. However, in recent years, various control devices installed in the vehicle assist deceleration control of the vehicle upon detection of a demand for deceleration of the vehicle (both a demand for deceleration based on the driver""s intention and a demand for deceleration based on other factors). Also, various control devices installed in the vehicle perform deceleration control of the vehicle. In this case, various control devices control a power train output (by reducing an engine output or performing a shift-down operation). In some cases, the hydraulic pressure generated by various control devices is transmitted to the wheels, whereby the vehicle is decelerated. Japanese Patent Application Laid-Open No. HEI 10-338056 discloses a device that performs such deceleration control. The device disclosed in Japanese Patent Application Laid-Open No. HEI 10-338056 is a follow-up traveling control device that automatically decelerates a vehicle in accordance with a distance between the vehicle and another vehicle traveling ahead of the vehicle.
However, if deceleration control is performed when the vehicle is making a turn close to a limit state, the vehicle may become destabilized causing the vehicle to skid or steer out of the control of the driver. For example, in the case where a rear-wheel-drive vehicle equipped with a follow-up traveling control device that controls a power train output to maintain a distance between the vehicle and another vehicle traveling ahead of the vehicle, deceleration control based on power train output control has an effect only on the driven rear wheels. If this vehicle is making a turn close to the limit state, the vehicle may be destabilized. However, deceleration control based on power train output control in a front-wheel-drive vehicle has an effect only on the driven front wheels. If the vehicle is making a turn close to the limit state, it may tend to deviate outwardly.
It is an object of the present invention to provide a vehicle deceleration unit that can stably decelerate a vehicle regardless of a turning state of the vehicle.
In order to solve the aforementioned problem, according to a first aspect of the present invention, there is provided a vehicle deceleration unit comprising a power train decelerator which controls a power train output to decelerate a vehicle and a brake device which presses a frictional member against a wheel or a rotational portion rotating together with the wheel to decelerate the vehicle, wherein the vehicle is decelerated by both power train output control based on the power train decelerator and brake control based on the brake device in a case of a demand for deceleration of the vehicle. The device comprises a target deceleration determiner which determines a target deceleration to be generated in the vehicle in a case of detection of a demand for deceleration of the vehicle, a turning state detector which detects a turning state of the vehicle, and a control amount calculator which calculates at least one of a power train output control amount of the power train controller and a brake control amount of the brake device based on the target deceleration determined by the target deceleration determiner and the turning state of the vehicle detected by the turning state detector.
The vehicle deceleration unit of the present invention detects the turning state of the vehicle, and calculates control amounts for power train output control and brake control based on the turning state and the target deceleration. Deceleration control of the vehicle is performed based on the control amounts for power train output control and brake control. Therefore, the vehicle may be stably braked.
Furthermore, the vehicle deceleration unit may further comprise a distance detector which detects a distance between the vehicle and another vehicle traveling ahead of the vehicle. The target deceleration determiner may determine a target deceleration based on the distance between both the vehicles detected by the distance detector. In this aspect, the distance between the vehicle and another vehicle traveling ahead of the vehicle is detected, and a target deceleration is determined based on the detected distance. Thus, it is possible to hold a following distance greater than a predetermined distance or prevent the vehicle from hitting another vehicle traveling ahead of the vehicle. If the vehicle is decelerated in such a case, the turning state of the vehicle is detected and taken into account during deceleration control. Therefore, the vehicle may be stably braked.
Also, the control amount calculator may determine a deceleration control distribution ratio between a driven wheel and a non-driven wheel based on the target deceleration determined by the target deceleration determiner and the turning state of the vehicle detected by the turning state detector. The control amount calculator may calculate a brake control amount and a power train output control amount of the driven wheel and may calculate a brake control amount of the non-driven wheel based on the determined deceleration control distribution ratio. In this aspect, it is possible to optimally balance deceleration through the driven wheel against deceleration through the non-driven wheel and decelerate the vehicle more stably, even when the vehicle is making a turn.
In addition, when calculating a brake control amount and a power train output control amount of the driven wheel, the setting of the power train output control amount may have precedence over the setting of the brake control amount. Therefore, it is possible to inhibit abrasion of the frictional members that are used during brake control and attenuate vibrations and noise generated by brake control.
Also, according to another aspect of the present invention, there is provided a vehicle control method comprising the steps of determining the target deceleration to be generated in the vehicle in a case of detection of a demand for deceleration of the vehicle, detecting the turning state of the vehicle, calculating at least one of the power train output control amount and the brake control amount based on the determined target deceleration and the detected turning state of the vehicle, and decelerating the vehicle based on at least one of the calculated power train output control amount and the calculated brake control amount.